ISAPI ⇝

Internet Server Application Programming Interface

(ISAPI) Microsoft's programming interface
between applications and their Internet Server. Active
Servers created with ISAPI extensions can be complete
in-process applications themselves, or can "connect" to other
services. ISAPI is used for the same sort of functions as
CGI but uses Microsoft Windowsdynamic link libraries
(DLL) for greater efficiency. The server loads the DLL the
first time a request is received and the DLL then stays in
memory, ready to service other requests until the server
decides it is no longer needed. This minimises the overhead
associated with executing such applications many times.

An HTTP server can unload ISAPI application DLLs to free
memory or preload them to speed up the first access.
Applications can also be enhanced by ISAPI filters